runtests: set web.address to localhost Previously, "hg serve" will listen on "", which is not clear which interface it will actually listen on - it could listen on all interfaces (ex. 0.0.0.0 on IPv4). The run-tests.py script only checks "localhost" for available ports. So let's make it the same for "hg serve" by explicitly setting "web.address" to "localhost". This resolves some IPv6 EADDRINUSE errors.